Crystal modifier and method for sol-vent separation of fatty materials

ABSTRACT

CRYSTAL MODIFIERS USEFUL IN THE SEPARATION OF MIXTURES OF MORE SATURATED FROM LESS SATURATED FATTY ACIDS OR MIXTURES OF RELATIVELY SATURATED AND RELATIVELY UNSATURATED TRIGLYCERIDES INTO SATURATED AND UNSATURATED FRACTIONS. ALSO A METHOD FOR CRYSTALLIZATION OF FATTY MATERIALS USING SAID CRYSTAL MODIFIERS. THE CRYSTAL MODIFIERS ARE PREPARED IN AN ACIDOLYSIS REACTION IN WHICH POLYBASIC ACIDS ARE REACTED WITH FATTY ACID ESTERS OF POLYHYDRIC ALCOHOLS.

United States Patent 3,776,928 CRYSTAL MODIFIER AND METHOD FOR SOL- VENT SEPARATION OF FA'ITY MATERIALS Donald D. Staker and Richard H. Plantholt, Cincinnati, Ohio, and David J. Kriege, Newport, Ky., assignors to Emery Industries, Inc., Cincinnati, Ohio No Drawing. Original application Apr. 5, 1968, Ser. No. 719,251, now Patent No. 3,649,657. Divided and this application Oct. 12, 1971, Ser. No. 188,530 Int. Cl. C07c 69/34, 69/80; C0811 9/00 US. Cl. 260404.8 8 Claims ABSTRACT OF THE DISCLOSURE Crystal modifiers useful in the separation of mixtures of more saturated from less saturated fatty acids or mixtures of relatively saturated and relatively unsaturated triglycerides into saturated and unsaturated fractions. Also a method for crystallization of fatty materials using said crystal modifiers. The crystal modifiers are prepared in an acidolysis reaction in which polybasic acids are reacted with fatty acid esters of polyhydric alcohols.

COPEN DING APPLICATION This application is a division of United States application Ser. No. 719,251, filed Apr. 5, 1968, now Pat. No. 3,649,657.

BACKGROUND OF THE INVENTION This invention relates to crystal modifiers and a method for crystallizing or separating fatty materials. More specifically, it relates to a method for separating more saturated fatty materials from less saturated fatty materials. The fatty materials may be in the form of fatty acids or esters such as glycerides.

Naturally occurring triglycerides, whether of animal or vegetable origin, in most instances contain both unsaturated and saturated fatty acid radicals. When the triglycerides are subjected to separating processes to produce free fatty acids, mixtures of saturated and unsaturated fatty acids are produced. The saturated fatty acids have a higher melting point than the unsaturated acid having the same carbon atom content. Because of this difference in melting points and other diiferences in properties between unsaturated and saturated acids, it is frequently desirable to separate the unsaturated acids from the saturated acids to obtain product fractions having greater commercial utility.

Historicallly, the most commonly used method of separating unsaturated acids from saturated acids on a commercial scale has been by pressing. The pressing method of separation is performed by cooling a molten mixture of acids without agitation until the mixture is partially solidified, then the resulting mass is enclosed in a porous bag or other filtering medium and subjected to mechanical pressure to force the liquid fraction through the filter medium. The pressing method is, at best, relatively inefficient in effecting a sharp separation. In order to obtain fractions of desired commercial purity, it is usually necessary to resort to three such cooling and pressing operations to achieve a high purity saturated acid fraction. Hence, the expression triple-pressed has come to be the conventional term for identifying stearic or other such saturated acids of high purity.

The pressing method, while having been used exten- 3,776,928 Patented Dec. 4, 1973 sively commercially, has many drawbacks. It requires considerable manual labor, is inefi'icient, and difficult to carry out. As a result, many attempts have been made in the past to effect separation of fatty acids on a continuous basis by other means including selective crystallization from a solvent medium. Generally, selective crystallization processes have been conducted using petroleum hydrocarbons such as propane and hexane or nonhydrocarbon solvents such as acetone and methanol. One of the principal difficulties with the prior solvent fractionation processes is the crystals formed when a solventfatty material mixture is chilled have been difiicult to filter at commercially practicable concentrations. Moreover, these crystals have included relatively large amounts of occluded unsaturated material and additional stages or crystallization steps have been required to obtain high purity products. In addition, high ratios of solvent to fatty material have been required, necessitating extensive solvent recovery systems, and unless the chilling was performed slowly with gradual crystal growth, a poor separation was obtained with the result that very large refrigerated chilling devices have been required.

The present invention provides an improved crystal modifier which enables highly effective separation of fatty materials of differing degrees of saturation such as stearic acid from oleic acid in a single crystallization step. It also enables the separation to be accomplished at a very low solvent to fatty material ratio thereby improving the economics of the separation process. It further provides a method whereby fatty material crystals are produced which can be easily separated from a solvent medium.

The crystal modifiers of this invention provide improved selective crystallization by promoting a denser type of crystal formation in the stearic acid or other crystallizable fatty material being selectively crystallized and make a more easily filterable and washable filter cake. More important, the use of these materials as crystal modifiers permits the use of higher concentrations of fatty acids in the solvent without any excessive thickness in the crystal slurry resulting, and this permits an increase in production rate for a plant of any given capacity. Without the use of a modifier, concentrations of not more than about 20 to 25% by weight fatty material in solution are feasible; however, when the crystal modifiers of this invention are used, concentrations of from 35 to 50% fatty material in solution may be employed in a plant. The difference in the crystal structure induced by the crystal modifier causes a thinner and less slimy and viscous crystal slurry than is formed without a" crystal modifier. The slurry is more esaily filtered and washed. This permits a higher percent solids in the filter cake and a firmer cake to be obtained and reduces the amount of solvent which must be distilled out of the cake.

DESCRIPTION OF THE INVENTION The present invention is concerned with crystal modifiers and an improved method for separation by crystallization of mixtures of fatty materials having differing degrees of saturation. The fatty materials which can be separated include long chain fatty acids such as stearic acid and oleic acid and glyceride fats and oils. The method of the invention is particularly applicable to the selective crystallization of saturated fatty acids from mixtures of saturated and unsaturated fatty acids obtained from glyceride materials of animal or vegetable origin, such as tallow or other fats and oils.

The crystal modifiers of this invention are polymeric esters which are prepared by the reaction of a polybasic acid with a fatty acid ester of a polyhydric alcohol.

The invention is practiced by forming a solution of the materials to be separated and the crystal modifier, and then cooling the solution to precipitate out the more saturated constituent.

Tht polybasic acids which may be used in the preparation of the crystal modifiers of this invention are aliphatic or aromatic polybasic acids, usually dibasic acids and some tribasic acids having from about 6 to about 54 carbon atoms. Specific examples of acids which may be used are phthalic acids, isophthalic acid, terephthalic acid, azelic acid, adipic acid, sebacic acid, and polymerized fatty acids which are commonly referred to as dimer acid and trimer acid. The latter two types of acids are generally made by polymerizing unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid, and have about 36 and 54 carbon atoms respectively.

The fatty acid esters which are used in the acidolysis reaction employed to prepare the crystal modifiers of the present invention may be glycerides of either animal or vegetable origin such as tallow or other fats and oils. The fatty acid moiety may be a saturated or unsaturated aliphatic fatty acid having from about 8 to 22 carbon atoms and the alcohol moiety may be a polyhydric alcohol having from about 2 to about 6 carbon atoms and from about 2 to about 6 hydroxyl groups. Specific examples of these polyhydric alcohols are ethylene glycol, propylene glycol, erythritol, glycerol, pentaerythritol, and sorbitol. The preferred fatty acid esters both from the standpoints of economics and crystal modifier performances which are produced are glycerides such as hydrogenated tallow and hydrogenated vegetable oils. The preferred polybasic acids for use in the acidolysis reaction to produce the crystal modifiers of this invention are the dibasic dimer acids having about 36 carbon atoms.

The amount of poly-basic acid which is reacted with the fatty acid ester to produce the crystal modifiers of this invention varies over a wide range and is dependent to a large extent upon the dibasic acid which is employed. Usually from about to 50% by Weight of polybasic acid, based on the total weight of the polybasic acid and fatty acid ester reactants, is used. Generally speaking, lesser amounts of the lower molecular Weight dibasic acids such as adipic, azelaic, or phthalic acid are required than dimer acid or trimer acid. The preferred crystal modifiers of this invention are prepared by reacting about 25- 35% by weight dimer acid with hydrogenated tallow when tallow fatty acids are separated, the amount of dimer acid being based upon the total Weight of the dimer and tallow.

The acidolysis reaction is performed by heating the polybasic acid and fatty acid ester in a reaction vessel at a temperature of about 250 to 300 C. usually under reduced pressure of about 1 to 5 mm. mercury. During the reaction of the polybasic acid replaces some of the monobasic acids in the glyceride structure and forms modifiers of this invention. The structure of the crystal modifiers is not known although they are believed to be higher molecular weight esters containing 2 or more polyol units. The physical form of the modifier is generally a waxy amorphous solid having a higher viscosity than the original mixture. The monobasic acids which are liberated in the reaction may be evaporated and collected by distillation. When approximately 70 to 90% by equivalent weight of the polybasic acid charged is removed in the form of monobasic acids in the distillate, the reaction is considered complete. The reaction may take place from about 3 to 24 hours depending upon the temperature used and the polybasic acid and fatty acid esters which are used in the preparation of the crystal modifiers. Shorter and longer periods can be used. Shorter period generally produce a less effective modifier and longer periods than about 24 hours do not enhance the quality of the modifier.

In one preferred embodiment of the present invention 35% by weight dimer acid based on the total weight of dimer acid and hydrogenated tallow is reacted at a temperature of 250 to 300 C. and at a pressure varying from 1 to 5 mm. mercury with the hydrogenated tallow for a period of 6 hours.

We have found in general that it is desirable to use as the ester reactant, one having as the fatty acid moiety a fatty acid of the same chain length as the chain length of the fatty acid fraction being crystallized. In other words, in the separation of stearic acid from oleic acid, it is preferable to use as the fatty acid ester of a polyhydric alcohol in the formation of the crystal modifier, a glyceride such as tallow which contains principally C fatty acids.

The separation process of the present invention is conducted by first forming a solution of the fatty materials which are to be separated into component fractions by selective crystallization. An organic solvent, preferably a polar organic solvent, is employed as a solvent medium. The crystal forming characteristics of the resulting solutions are such that, with most fatty materials, the concentration of fatty material in the starting solution should not exceed about 35 to 50% by Weight of the solution if good results are to be obtained during the crystallization and, more particularly, the crystal separation and washing steps. As the fatty material concentration materially exceeds about 50%, the crystal mass formed on cooling the solution tends to become slimy in character and is difficult to handle. Filtering of the crystals is slow, as are subsequent washing steps. Moreover, the washed saturated acid, e.g. stearic acid filter cake, tends to be contaminated with an undue proportion of unsaturated acids, e.g. oleic acid. Further, processing may be required if the oleic acid content is too high. The ratio by weight of solvent to fatty material can vary over a range of about 1:1 to about 3:1, with the lower solvent to fatty material ratios being preferred.

After the solution of the fatty material to be separated into its component fractions and modifier has been formed, the solution is chilled. The amount of crystal modifier to be employed will normally range from about 0.2 to 3% based on the weight of fatty material present in the solution, with a preferred range being from 0.5 to 1.5% by weight. Amounts greater than 3% by weight of crystal modifier can be employed successfully; however, increasing the amount of crystal modifier to such levels provides little if any benefit over and above results which are obtainable at 3% or less.

The actual separation of the fatty material into its component fractions is carried out by chilling the solution containing a crystal modifier to a temperature below the precipitation temperature of the saturated fatty material in the solvent. A sharp separation of the saturated fatty material occurs, the saturated material precipitating in the form of readily filterable crystals.

The separation can be effectively performed in a scraped surface heat exchanger such as the type sold under the trade name Votator. In this type of heat exchanger, the solution is rapidly chilled from a temperature of as high as 35 C. to a temperature at which the more saturated fatty material precipitates in the form of crystals, usually a temperature of about 10 C. The precipitated crystals are collected on a filter forming a filter cake and then are washed by solvent. The filter cake is collected and evaporated leaving the saturated fatty material.

The unsaturated components of the fatty material mixture remain in solution and are collected as a filtrate. Evaporation of the filtrate enables recovery of the unsaturated components.

As was indicated above, the solvent used in the separation process of this invention should be an organic solvent, preferably a polar organic solvent. A number of solvents may be employed including low molecular weight alcohols, ketones, nitroalkanes, esters, nitriles, amides, and hydrocarbons. Specific examples of solvents which are useful in the present invention are methanol, ethanol, acetone, 2-nitropropane, l-nitropropane, isopropyl acetate, acetonitrile, dimethyl formamide and hexane. The preferred solvent depends upon the fatty material to be separated and the specific method of separation. For most purposes, methanol is preferred with acetone being the next most preferred solvent.

The following examples are provided to further illustrate the invention, but are not to be construed as limitative of the scope thereof.

Examples 1 to 18 A number of crystal modifiers of this invention were prepared in an acidolysis reaction by reacting polybasic acids with fatty acid esters of polyhydric alcohols. The acidolysis reaction was performed by charging the polybasic acid and fatty acid ester of a polyhydric alcohol into a reaction vessel and heating the reactants for an extended period of time of from about 3 to hours. During the reaction, monobasic acid was liberated and it was removed from the reaction and collected by distillation. The reactions for the most part were conducted at temperatures ranging from about 250300 C., the lower temperature range being generally used initially with the temperature being allowed to increase as the reaction progressed. In Example No. 15, in which phthalic anhydride and a mixed glyceride were used to prepare the crystal modifier, a solvent, toluene, was used to aid the reaction. The crystal modifier shown in Example 17 was prepared by reacting the azelaic acid and hydrogenated tallow at a temperature of 250 C. and at a pressure of about 35 mm. mercury for 5 hours. The monobasic acids which were formed during the reaction were then stripped at a temperature of 1 to 5 mm. mercury and at a temperature of 250300 C. The crystal modifier shown in Example 18 was prepared by reacting the adipic acid and hydrogenated tallow for 4 hours under a carbon dioxide blanket at 240 C. The monobasic acids formed in that acidolysis reaction were stripped at the end of the 4 hour period at a pressure of 1 to 5 mm. mercury and at a temperature of 250 C.

6 Examples 19 to 51 A number of tests were conducted to determine the effectiveness of the crystal modifiers shown in Table I in the separation of fatty acid mixtures into their compo nent fractions. The results of these tests are shown in Table II. The crystal modifier type shown in Table II refers to the example number of the modifier shown in Table I. The tests were conducted by first forming a solution of a fatty acid mixture, the crystal modifier, and a solvent, either methanol, acetone or Z-nitropropane. The resulting solution was then cooled in a stirred, scraping crystallizer to from about 0 C. to about 20 C. depending upon the solvent and the fatty material to be removed. The resulting slurries were then filtered using a Buchner funnel while maintaining a vacuum of 5 p.s.i. until no liquid layer was visible above the crystalline layer. The resulting filter cake was then washed using 200 parts by weight of the solvent which was used to form the solution for each 100 parts of the solid cake in the funnel.

Various tests were run on the washed filter cake to determine (1) its content of solids, (2) its yield, and (3) the iodine value of the filter cake solids. The solvent was removed by heating on a steam bath followed by drying on a hot plate. A high solids content in the cake is desirable, for this indicates a correspondingly low content of solvent to be evaporated and returned to the crystallizer unit. One of the most significant features of this invention is the high percentage of solids in cake which are achieveable. A low iodine value is desirable because it indicates the effectiveness of the separation process, a low content of occluded unsaturated acid in the washed and dried solids fraction showing good separation. In the runs involving separation of tallow fatty acids, an iodine value of approximately 8-11 is regarded as satisfactory, though the values obtained in plant use might run somewhat higher (or lower), depending upon the nature of the equipment employed, and the severity of the washing step (s).

Table I.PREPARATION OF CRYSTAL MODIFIERS Percent by wt. of Polypolybasic basic Fatty acid ester of polyhydric alcohol acid based acid on total Time of wt. Wt. wt. of reaction, (grams) Type (grams) Type reactants hrs.

335 Hydrogenated tallow 35 4 375 do 25 4 300 do 10 800 Hydrogenated stearic acid 10 2. 5

residue 8 2O 5. 5 l0 3 10 6 10 9 95 d0 5 5 400 Hydrogenated tallow 33 8 345 ....do l2. 5 6 21 6 20 6 33 3 500 Mixed glycerlde l8 4 288 Ethylene glycol distearate.-. 15 5 850 Hydrogenated tallow 18 5 320 .do 17 4 1 Dimer acid used was Empol 1018, a polymerized tall oil fatty acid having about 83% by weight 036 dibasie acid and about 17% by weight 054 tn'basic acid.

1 The trlmer acid used was Empol 1040, a polymerized tall oil fatty acid having about -90% by weight 054 tribasic acid and 10-20% by weight Cu dibasic acid.

3 Stealic acid residue is a mixture containing predominantly monoglycerides, diglycerides, triglycerides and polymerized glycerides plus small amounts of stearic acid remaining as residue after the distillation of stearic acid A mixture of 25% monoglycerides, 50% diglycerides, and 25% triglycerides.

TABLE 11 Amount Percent of crystal Percent by wt. iyield of Crystal modifier more satumodifier used in Fatty rated comfrom Filtration wt. per- Solids in material in ponent by Iodine Example number Table I Feedstock Solvent temp., 0. cent cake solution wt. value 1 Undistilled PFA Methanol 10 1 69.67 3 do d 10 51.8 1 Hydrogenated tall oil --10 1 54. 3 1 Undistiiled PFA -10 0.5 52. 1 1 -10 1. 5 63.7 1 Distilled PFA 1 44. 8 2 o 10 1 41.5 None Flashing greas 10 None 26. 0 1 do -10 1 61.0 10 1 34. 2 1 63. 6 --20 1 46. 0 None -.do 0 None 17.4 0 1 21. 0 -10 1 21. 1 10 1 51. 8 -10 1 59. 3 -12 1 32.0 10 1 57. 7 ---10 1 69. 4 -10 1 47.3 10 1 65.2 10 1 69. 8 10 1 68. 4 10 1 65.3 10 1 32.5 10 1 61. 2 10 1 54. 7 10 1 63.3 -10 1 47. 5 10 1 64. 2 10 1 65. 0 -10 1 38.4

1 Pressure split fatty acids. 1 92.5% by weight methanol, 7.5% water.

3 The C15 fatty acid distillate recovered from polymerization of tall oil fatty acids.

4 Hydrogenated tallow.

l Hydrogenated stearic acid residue.

2-nitro-propane.

From the data presented in Table II above, it may be seen that the crystal modifiers of the present invention enable the use of solutions having a far greater concentration of fatty acid than would otherwise be possible, while still obtaining a solid phase which filters well, is high in solids content, has a good yield, and has a desirably low iodine value.

The present process can also be used in the separation of unsaturated acids such as oleic acid from more unsaturated acids such as linoleic acid or linolenic acid, and it is useful in the separation of more saturated fractions from less saturated fractions of glycerides and like materials.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made Without departing from the spirit and scope thereof, and therefore, only those limitations should be imposed as are indicated in the appended claims.

We claim:

1. A polymeric ester having crystal modifier properties comprising the reaction product by acidolysis of a polybasic acid having from about 6 to 54 carbon atoms and an ester of a polyhydric alcohol and a fatty acid, said fatty acid having from about 8 to 22 carbon atoms.

2. The polymeric ester of claim 1 wherein said polyhydric alcohol has from 2 to about 6 carbon atoms and from 2 to about 6 hydroxyl groups.

3. The polymeric ester of claim 2 wherein said ester is a glyceride.

4. The polymeric ester of claim 3 wherein said polybasic acid is selected from the group consisting of adipic acid, sebacic acid, phthalic acid, azelaic acid, and polymerized unsaturated fatty acids.

5. The polymeric ester of claim 4 wherein said polybasic acid is a polymerized unsaturated fatty acid.

6. A method for preparing the crystal modifier of claim 1 which comprises reacting said polybasic acid and said ester at a temperature of about 250 C. to 300 C. [for a period of at least about three hours.

7. The method of claim 6 wherein said polybasic acid is polymerized unsaturated fatty acid.

8. The composition of claim 1 wherein the polybasic acid residue comprises from 5 to 50% of the polymeric ester.

References Cited UNITED STATES PATENTS 2,874,175 2/1959 Feuge et a1 260404.8 3,035,923 5/1962 Geisler 99148 Re. 25,696 12/1964 Houben et al. 99'-123 2,552,706 5/1951 Bertram 252312 2,966,412 12/1960 Gleason 991 18 OTHER REFERENCES Condensed Chemical Dictionary, 6th ed. Reinhold Publishing Corp., N.Y., p. 484 (1961).

LEWIS GOTIS, Primary Examiner D. G. RIVERS, Assistant Examiner US. Cl. X.R. 260407, 413 

